Methyl (2R,3R)-2-{3-[amino(imino)methyl]benzyl}-3-{[4-(1-oxidopyridin-4-yl)benzoyl]amino}butanoate (CAS number 193153-04-7) has the international nonproprietary name Otamixaban and shows the structure illustrated in Formula I:

Methyl (2R,3R)-2-{3-[amino(imino)methyl]benzyl}-3-{[4-(1-oxidopyridin-4-yl)benzoyl]amino}butanoate use in the preparation of a medicament for treating a patient suffering from, or subject to, conditions which can be ameliorated by the administration of an inhibitor of Factor Xa was disclosed in WO97/24118.
Factor Xa is the penultimate enzyme in the coagulation cascade. Factor Xa (fXa) is a critical serine protease situated at the confluence of the intrinsic and extrinsic pathways of the blood coagulation cascade. FXa catalyses the conversion of prothrombin to thrombin via the prothrombinase complex. Its singular role in thrombin generation, coupled with its potentiating effects on clot formation render it an attractive target for therapeutic intervention.
Both free factor Xa and factor Xa assembled in the prothrombinase complex (Factor Xa, Factor Va, calcium and phospholipid) are inhibited by Otamixaban. Factor Xa inhibition is obtained by direct complex formation between the inhibitor and the enzyme and is therefore independent of the plasma co-factor antithrombin III. Effective factor Xa inhibition is achieved by administering the compound either by continuous intravenous infusion, bolus intravenous administration or any other parenteral route such that it achieves the desired effect of preventing the factor Xa induced formation of thrombin from prothrombin. In vivo experiments have demonstrated that Otamixaban is highly efficacious in rodent, canine and porcine models of thrombosis. In addition, recent clinical findings indicate that Otamixaban is efficacious, safe and well tolerated in humans and therefore has considerable potential for the treatment of acute coronary syndrome (K. R. Guertin and Yong-Mi Choi; 2007; Current Medicinal Chemistry, Vol. 14, No. 23; p. 2471-2481). Clinical findings in a dose-ranging clinical trial indicate that Otamixaban reduced prothrombin fragments 1+2 significantly more than unfractionated heparin at the highest dose regimen (Cohen et al., Circulation, Vol. 115, No. 20, May 2007, pages 2642-2651), but said clinical findings do not show data in comparison of age or renal impairment. Further clinical trials demonstrated that Otamixaban induces dose-dependent, rapid direct factor Xa inhibition in patients with stable coronary artery disease who are taking their usual comedication, some of whom have mild renal impairment (Hinder et al., Clinical Pharmacology and Therapeutics, Vol. 80, No. 6, 2006, pages 691-702).
An injection and infusion pharmaceutical composition for (methyl (2R,3R)-2-{3-[amino(imino)methyl]benzyl}-3-{[4-(1-oxidopyridin-4-yl)benzoyl]amino}butanoate was developed for use in clinical studies. One of the observations made during terminal sterilization (autoclaving) and stability studies was a strong increase in two degradants. One of said degradants is (2R,3R)-2-(3-Carbamimidoyl-benzyl)-3-[4-(1-oxy-pyridin-4-yl) benzoylamino]-butyric acid and has the structure illustrated in Formula II:

The other of said degradants is (2R,3R)-2-(3-Carbamoyl-benzyl)-3-[4-(1-oxy-pyridin-4-yl)benzoylamino]-butyric acid methyl ester and has the structure illustrated in Formula III:

At recommended storage conditions also elevated levels of (2R,3R)-2-(3-Carbamimidoyl-benzyl)-3-[4-(1-oxy-pyridin-4-yl)benzoylamino]-butyric acid and (2R,3R)-2-(3-Carbamoyl-benzyl)-3-[4-(1-oxy-pyridin-4-yl)benzoylamino]-butyric acid methyl ester are reached in an aqueous pharmaceutical composition containing methyl (2R,3R)-2-{3-[amino(imino)methyl]benzyl}-3-{[4-(1-oxidopyridin-4-yl)benzoyl]amino}butanoate.
It is an object of the present invention to find a long term stable pharmaceutical composition for methyl (2R,3R)-2-{3-[amino(imino)methyl]benzyl}-3-{[4-(1-oxidopyridin-4-yl)benzoyl]amino}butanoate which does not have the disadvantages of increased concentrations of (2R,3R)-2-(3-Carbamimidoyl-benzyl)-3-[4-(1-oxy-pyridin-4-yl) benzoylamino]-butyric acid or (2R,3R)-2-(3-Carbamoyl-benzyl)-3-[4-(1-oxy-pyridin-4-yl) benzoylamino]-butyric acid methyl ester which occur during terminal sterilization or long term storage.
It has been found that the formation of (2R,3R)-2-(3-Carbamimidoyl-benzyl)-3-[4-(1-oxy-pyridin-4-yl)benzoylamino]-butyric acid or (2R,3R)-2-(3-Carbamoyl-benzyl)-3-[4-(1-oxy-pyridin-4-yl)benzoylamino]-butyric acid methyl ester during long term storage of the drug product is determined by opposite effects:                During autoclaving, the levels of (2R,3R)-2-(3-Carbamoyl-benzyl)-3-[4-(1-oxy-pyridin-4-yl)benzoylamino]-butyric acid methyl ester increase significantly with increasing pH of the liquid pharmaceutical composition, whereas no strong influence of the pH of the liquid formulation on formation of (2R,3R)-2-(3-Carbamimidoyl-benzyl)-3-[4-(1-oxy-pyridin-4-yl) benzoylamino]-butyric acid was observed during autoclaving. In conclusion: The lower the pH of the pharmaceutical composition the better!        During long term storage, the levels of (2R,3R)-2-(3-Carbamimidoyl-benzyl)-3-[4-(1-oxy-pyridin-4-yl)benzoylamino]-butyric acid increase significantly with decreasing pH of the liquid pharmaceutical composition, whereas no strong influence of the pH of the liquid formulation on formation of (2R,3R)-2-(3-Carbamoyl-benzyl)-3-[4-(1-oxy-pyridin-4-yl)benzoylamino]-butyric acid methyl ester was observed during long term storage. In conclusion: The higher the pH of the pharmaceutical composition the better!        
It has been found that liquid pharmaceutical compositions for methyl (2R,3R)-2-{3-[amino(imino)methyl]benzyl}-3-{[4-(1-oxidopyridin-4-yl)benzoyl]amino}butanoate or a pharmaceutically acceptable salt thereof with a pH below 5 are advantageous with respect to limiting the increase in both (2R,3R)-2-(3-Carbamimidoyl-benzyl)-3-[4-(1-oxy-pyridin-4-yl)benzoylamino]-butyric acid and (2R,3R)-2-(3-Carbamoyl-benzyl)-3-[4-(1-oxy-pyridin-4-yl)benzoylamino]-butyric acid methyl ester, influenced oppositely by autoclaving or long term storage.
A pH below 5 provides the clear advantage of the pharmaceutical compositions according to the invention which are (i) long term stable pharmaceutical compositions and (II) sterile injection solutions by autoclavation (steam sterilization), which is a simple, economic and safe method for sterilization.